Control system.



A.J,HALL

CONTROL SYSTEM.

APPLICATION FILED APR.25.I914. RENEWED JUNE 19,191L

Patented Nov. 6, 1917.

3 SHEETS-SHEET I.

Raver-sen BY Z2 ATTORNEY .J. HALL. CONTROL-SYSTEM.

APPLICATION FILED APR.25| i914- RENEWED JUNE I9, 1917- Patented Nov. 6, 1917.

3 SHEETS-SHEET 2.

WITNESSES:

ATTORNEY A. J. HALL.

CONTROL SYSTEM.

APPLICATWN HLED APR. 25, m4. RENEWED IUNE 19. um.

1 245,223. Patented Nov. 6, 1917.

3 SHEETS-SHEET 3.

00/ III? 8/?! 6rol;nd

WITNESSES INVENTOR 3Z4. Ara/Ur J //a// v ATTORNEY UNITED STATES PATENT OFFICE.

ARTHUR J. HALL, OF WILKINSTBURC, IBENNSYLVANIA, ASSIGN'OR T0 WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF IENNSYLVANIA.

conrnon svsrmc.

Specification of Letters Patent.

Patented Nov. 6, 191'7.

Application filed April 25, 1914, Serial No. 834,545. Renewed June 19, 1917, Serial No. 175,713.

To all whom it may concern:

Be it known that I, ARTHUR J. HALL, a subject of the King of Great Britain, and a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Control Systems, of which the following is a specification.

My invention relates to systems of electric motor control, and it has'special reference to such systems as are adapted for use in electric railway service. 4 y

Another object of my invention is to provide an automatic control system of the regenerative type wherein the control circuits are simplified, in comparison with prior systems of the same general class.

Another object of my invention is to provide particularly simple, effective and reliable means for automatically maintaining a substantially constant regenerated current as the motor speed decreases, whereby peaks oi current are eliminated, even upon a sudden drop of line voltage, and whereby certain circuit changes are accomplished more rapidly and positively than heretofore, thus increasing the efficiency of the system, as hereinafter explained in detail.

A further obgect of my invention is to provide an automatic control system of the above-indicated character which shall embody all the well-known advantages of regenerative control in a higher degree than has obtained in the prior art.

While m invention is articularl ada t- Y P J, P

ed for the control of railway vehicles, it

is not'limited to any class of service and may be utilized in the control of automobiles and other road vehicles, or in the control or cranes, hoists and other electrically-operated devices. My system is also especially applicable to multiple unit train systems of con.- trol.

"in order to adapt the system of control for this class oi service and to secure a maximum braking effort without injuring the electric motors or the other apparatus with which the vehicle is equipped, I have rovided automatic means, in the form of a differential relay switch, for automatically.

connecting a motor to the supply circuit when the electromotive force generated at its terminals bears a predetermined relation to the voltage of the supply circuit,

I also employ automatic means for regulating the field excitation of the motor during the regenerative period, whereby a substantially constant braking current is delivered to the supply circuit. The means in. uestion comprises a main line switch that is adapted to insert in circuit, or to shortcircuit, a predetermined resistance, the switch being controlled through a high-current limit switch, thus inserting resistance when the current tends to increase beyond a predetermined amount and short-circuiting the resistance at other times, as broadly claimed in a hereinafter identified co-pending application. 1 also employ other automatic step-by-step means for regulating the field current during the braking period, such as is described in the co-pending application of Norman W. Storer, Serial No. 724:,068, filed @ctober 5, 1912, and assigned to the Westinghouse Electric and Manufacturing Company. In operation, it has been found that the short-circuiting switch referred to above flutters open and closed like the regulating contact member of a Tirrill regulator, thus serving to maintain a substantially constant current, in a well-known manner.

accelerating the vehicle, by adjusting the master controller in one d1rect1on, and of automatic adjustment of the circuits for regenerative braking accompanied by independent connection 01 the motors to the circuit at the proper time, by throwing the master controller in the opposite direction. Moreover, if desired, automatic application of air brakes, when the field regulation has reached its limit and the vehicle speed is relatively low, may readily be accomplished, as disclosed in the above-mentioned pendingapplication.

Figure 1 of the accompanying drawings is a diagrammatic view oi a system of electric motor control embodying my invention, the main circuit connections and the switches and control apparatus which are directly associated therewith being shown complete accordingto the usual diagrammatic methods of representation. The control circuits are, however, indicated merely by appropriately designated lines, in order to avoid confusion. V

Fig. 2 is a diagrammatic view of the con- In addition to the foregoing, l have so ineach of them is marked to indicate the switch or control. device with which it is associated and by'which itis operated.

Fig. 3, Fig. 4' and Fig. 5 are simplified diagrammatic views that respectively correspond to acceleration with the motors in series relation, acceleration with the motors in parallel relation, and regeneration of the momentum-driven machines.

Referring to Fig. 1 of the drawings, the system here shown comprises a supply circuit conductor which, for convenience, is marked Trolley; a return circuit conductor which is marked Ground; a pair of electric motors having armatures marked, respectively, M#1 and M#2,-and field magnet windings marked, respectively, F1 and F2; two LS1, M2 and LS2; a: resistor section used only when the motors are connected in series relation and adapted to be short-circuited by a switch S; a plurality of resistor sections that are adapted to be respectively short-circuited by switches R1, R2 and R3; a second group of resistor sections that are adapted to be respectively short circuited by switches RRl, RR2 and RR3; a pair of step-by-step field-regulating resistances FRI and FR2; a second pair of field-regulating resistances that are adapted to be respectively short-circuited by switches RX and RY; a pair of switches X1. and X2 for respectively short-circuiting the pairs of resistances FRl and RX and FR2 and RY;

storage batteries marked respectively Bat. 1 and Bat. 2; a pair of controllers for governing the step-by-step field-regulating resistances, marked PKl and PK2; a plurality of limit switches comprising D, B and C in one group, and G, E and F in another group; a plurality of control switches JR, J and G; an overground trip relay switch OT; differential relay switches D1 and D2; a field change-over switch FC; and a reversing switch marked Reverser.

In' order to avoid confusion, each resistor section will hereinafter be designated by the reference character which is applied to its short-circuiting or excluding switch, for ex ample; the resistor short circuited by the switch S will be termed the S-resistor. Similarly, one of the motors will be referred to as motor M#1, which is the reference character applied to its armature, and, the other as motor M#2.

The operation of the system with reference to the main circui'ts'only will first be discussed and, subsequently, the control cirpair of line switches marked M1,.

cuits, by which the desired circuit changes are accomplished, will be traced.

Assuming that it is desired to accelerate the motors, switches M1, LS1, LS2, JR and X1 and X2 are first closed, thereby estabthe switches M1 and LS1, the series resistor S, the coils of limit switches D, B, and C, the armature M#1, the full field magnet winding F1 by -means of certain contact members of the reverser, the switch X1, resistor sections R1, R2 and R3, switch JR, resistor sections RRl, RR2 and RR3, the coils of limit switches G, E and F, the arms.- ture M#2, the full field magnet winding F2, by means of certain contact members of the reverser, the switch X2, and the coil of the overload trip switch OT to the ground. The motors are thus connected in series, with all of the resistor sections included in the circuit, with the exception of the fieldregulating resistor sections, which are shortcircuited. Fig. 3 shows the circuit connections at this time.

The resistor sections are then gradually short-circuited to increase the motor speed. When full series position has been reached, the field changeover switches are operated to make the normal field connection in a well known manner.

The transition from series to parallel is of the familiar bridging type, in so far as the main circuits are concerned, the resistance switches being opened during the transition.

The resistor sections are then again gradually short-circuited and the motors brought to full parallel position, whereupon the field change-over switches are again actuated to .the normal field position. The simplified opened and a plurality of switches Y1 and Z1 and Y2 and Z2 are closed. Inasmuch as the line switches LS1 and LS2 are open, the motors are not connected to the line. However, Bat. 1 is connected in shunt relation regulating resistance FRl, while Bat. 2 is similarly connected in parallel with the field magnet winding F2 and the field regulating-resistance FR2.

The line switches LS1 and LS2 are automatically and respectively dependent upon the differential relay switches D1 and D2 and, consequently, when a' predetermined relation exists between the voltages gento the field magnet winding F1 and the field- 70 lishing a circuit from the trolley, through the motors are automatically and independ ently connected to the line by the closing of the corresponding line switches LS1 and LS2. After the motors are connected to the circuit, the series resistances are short circuited, and the controllers PKl and PK2, in conjunction withithe switch having the Tirrill regulator action, are automatically regulated, as hereinafter pointed out, to so governthe field-regulating resistances with which they are associated as to maintain a substantially constant braking current. This obviously involves the gradual exclusion of the regulating resistances in order to maintain substantially constant generated volt ages at the terminals of the motors, as their speeds decrease.

The PK controllers are intended to be representative of any suitable means for automatically governing the field-regulating resistances and I do not wish to be limited to any specified control apparatus.

Each of the PK controllers comprises a plurality of contact fingers which are connected to intermediate points in the fieldregulating' resistor with which it is associated; suitable contact segments which are adapted to successively engage the fingers and gradually short-circuit the resistance in a well-known manner; contact members for forming parts of the switches Y and Z; and a plurality of interlocking'contact members and fingers cooperating therewith, which will be .re'ferredto in detail in the discus sion of the control circuits.

Each of the controllers is preferably in the 'form of a drum, which is shown developed into a single plane in a well known manner, and is provided with a shaftv 1 to which a pinion 2 is secured. Each of the drums is actuated by a rack 3 which meshes with its pinion 2 and is connected, at its respective ends, to pistons l and 5 which operate in cylinders 6 and 7. Fluid pressure is admitted from a tank or reservoir 8, through an electromagnetically controlled valve 9, to the cylinder 7, when an actuating coil 10 for the valve is deenergized, and fluid pressure is admitted from the tank or reservoir to the cylinder 6, when an actuating coil 11 for the other magnet .valve 12 is energized.

lhe arrangement of parts is such that, if both magnet valves are de'e'nergized, fluid pressure will be admitted through the valve 9 to the cylinder 7 and will so actuate the pistons 4 and the rack 3 as to throw the PK drum, with which it is associated, to its ofi'. position.

If the valve magnet 12 is energized, fluid pressure will be admitted to the cylinder 6, but no motion of the drum will result, inasmuch as the pressures are then balanced on the two sides of the piston member. A motion of the drum may be produced, however, by subsequently energizing the coil 10 of the valve 9, since, by this means, the valve 9 will cut off the supply of pressure from the reservoir and will open its exhaust port. The drum may be stopped at any position by merely deenergizing the coil 10, and it may be returned to its off position by merely deenergizing both of the coils 10 and 11.

The valve magnet 12 which, when ener-.

gized, is open to admit fluid pressure to the cylinder and, when deenergized is closed to exhaust air from the cylinder, will hereinafter be referred to as a standard valve magnet, while the valve magnet 9, which is open to admit fluid pressure to the cylinder when deenergized, and exhausts the air from the cylinder when energized, will hereinafter be referred to as an inverted valve magnet.

The reverser may be of any suitable type, but preferably comprises a drum sec-. tion which is adapted to occupy two positions, one for forward and the other for reverse operation of the vehicle. It is pret erably pneumatically operated, and is con-. trolled by valveshaving actuating coils 13 value, and the switches D, B, G and E are opened when energized above predetermined values.

Each of the difi'erential'relay switches D1 and D2 is provided with a coil 15 which, when energized, tends to raise it, and a coil 16 which tends to hold it down.

The coils 15 are respectively connected in shunt relation to the armatures M1 and M2 when the PK drums occupy any on position, of which, for illustrative purposes, 1 have shown eight, by reason of the engagement of contact fingers 17 with a contact member 18. The'coils 16 are similarly connected across the supply. circuit in the on position of the PK drums, by reason of the engagement of contact fingers 19 with a contact member 20.

Referring to Fig. 2 of the drawings, the ..1

control circuits here shown are governed by a. master controller that is adapted to occupy an"off position, accelerating positions, 1, 2 and 3, a holding position 1 and a braking position 2; and a master reverser that is adapted to occupy a forward position 7 and a reversing position a".

Energy may be supplied to the control circuits from any suitable source, such as a control battery having a positive terminal Which, together with its connected conduc-- tors, is markedB+ and a negative terminal which, with its connected conductors, is marked B.' I

The arrangement of circuits is such that,

relation. If the master controller is moved only to position 2, the acceleration will progress until the motors are connected across the line in series relation and, if moved only to position 1, the motors will be connected in series relation across the line, with all the accelerating resistance in series. 7 It is thus evident that automatic acceleration is provided for, but that the progression may be'delayed at several points, according to the will of the operator.

Assuming that the master controller is moved from its oil position to its accelerating position 3; that the master reverser has been thrown into its position 7, and that the reverser occupies its position 0, a control circuit is established from the control battery terminal and conductor 13+, control fingers 21 and 22, which are bridged by a contact member 23 of the master reverser, contact'fingers 24 and 25, which are bridged by a contact member 26 of the master con-- troller, conductor 27, control fingers 28 and 29, which are bridged by a contact member 30 of the master reverser, conductor 31, control fingers 32 and 33, which are bridged by a contact member 34 of the reverser, the forward coil 13 of the reverser, and the interlock marked M1 out to the negative control conductor B--. The reverser is thus thrown to the forward position.

A circuit is thereupon established from the contact member 34, through a control finger 35, conductor 36, stationary auxiliary contact member of the overload trip OT, conductor 37 and the coil of the switch M1 to the conductor B, the switch being thus closed.

Another circuit is established from an energized contact member 38 of the master controller through conductor 39, two parallel circuits, one of which includes an interlock marked PKl off and the coil of the line switch LS1 and the other of which includes an interlock marked PK2 ed and the coil of the line switch LS2, and then through a common interlock marked M1 in to the control conductor B. Also, a circuit is completed from the conductor 39 through an interlock marked G out, the

coil of the switch JR, a conductor 40, an interlock marked J out and to the conductor B-. In this way, the line switches LS1 and LS2 and the switch JB are closed, and the motors are connected across the line, with all the accelerating resistance in series.

Then the current has dropped below a predetermined value for which the limit switch B is set, the switch assumes its lower position, and acircuit is established from an energized contact member 41 of the iconconductor 52, contact member 53 of the switch S and the coil of thatswitch to the conductor B-. When the switch S is closed, a circuit is progressively made through the coils of switches B1, -B2 and B3 to the conductor 40, dependent upon the limit switch B, in accordance with familiar practice, the magnet coils, after closure of the switches, being transferred to the holding conductor 37.

A similar circuit is also established from the control finger 46 of the field changeover switch, through auxiliary contact members of the limit switch E an'd an interlock marked LS2-in to the coils of the switches BB1, BB2 and BB3, which are thus also closed. Other circuits are respectively established between the of the switches B1 and BB1, 2 and BB2, B3 and BB3, each of these circuits including series-connected interlocks marked FPKl off and PK2 off,- thereby insuring the closure of the BB1 set of switches substantially simultaneousl I with the corresponding switches of the 1 set, unless the encrairs of coils;

gization of the BB1 set through the limit switch E has caused a prior closure-of that set. The resistances are thus short-circuited as rapidly as is consistent with good operation, thus increasing the efiiciency of acceleration. As a means of obtaining further increase of etiiciency, after the resistances are all short-circuited the field changeover switch is actuated to its normal field position by the energization of the magnet coil of the switch from a contact member 54 'of the switch BB3, through contact member 55 of the field change-over switch, and interlock marked PK2 off. The motors are thus connected in full series relation with normal field connection.

When the field change-over switch is actuated, a circuit is established from an energized contact member 56 of the master controller, through a control finger 57,conductor 58, the contact member 47 of the field change-over switch, stationary contact members of the limit switch B, when it occupies its lower position, the contact member 50,-

interlock marked J out in the conductor 40. A circuit is then established from the conductor 58, through a conductor 59, interlock marked Jin, interlock marked Ch. 0. F..F., meaning change-over switch full field, conductor 60, stationary auxiliary contact members or the overload trip OT, interlock marked JR out, and the coils of the switches M2 and G to the conductor B-. Upon the closure of the switch M2, the switch J is opened, by reason of the inclusion in its control circuit of the interlock marked M2 out. It will thus be seen that themotors have been changed from series to parallel connection by means of the fa- .miliar bridging transition, in so far as the main circuits are concerned. When the swltch J drops out, the above-mentioned control circuit of the switches M2 and G is opened at the point marked J-ouit, but a new circuit is established from the conductor 36, through a conductor 61 and an interlock marked M2in to the conductor 60.

As soon as the switch G is closed, a circuit is completed between the conductors 43 and 4:4 by means of an interlock marked Gin. The coils of the switches R1, R2,

R3, BBL-BB2, BB3, and the field change- .over are then energized, as hereinbefore described, the motors being finally disposed in full parallel relation, with normal field connection.

It will be observed that the holding circuit of the switch Sis independent of the position of the switch J and, consequently,

- the switch S remains closed during the complete operation ofthe controller, after it has once been actuated.

A substantially balanced relation is maintained between the two parallel motor circuits by reason of the fact that the control circuits of the corresponding switches of the two motor circuits are tied to each other, as hereinbefore described, thereby insuring similar main circuit conditions and equal division of the load.

Referring to the regenerative circuits, let it be assumed that the vehicleis being propelled by the motors at or above a predetermined rate of speed, and that the master controller is returned to its of position, permitting all the switches to open, and is moved to its braking position; under these conditions, energy is supplied from the energized control finger 24 to a control finger 62, which fingers are connected by contact members 63 and 6.4 of the master controller, conductor 65, control fingers 66 and 67, which are bridged by a contact member 68 of the master reverser, conductor 69, control fingers 70 and 71, which are bridged by a contact member 72 of the reverser, the reverse coil 14 thereof, and the interlock marked M1 out to the conductor B. The reverser is thus thrown to its reverse position without operating the master reverser. Upon actuation of the reverser, a circuit is established from control fingers 70 and 73, which are now bridged by the contact member 72, conductor 74 and conductor 36 to the coil of the switch M1, which is thus closed.

Another circuit is established from an energized contact member 75 of the master controller, through a control finger 76, and conductors 77 and 78, where the circuit divides, one branch including a contact member marked PKl off and the inverted valve magnet of PKl controller and also including a contact member marked PKZ ofi and the inverted valve magnet of PR2 controller, the two magnet valve coil circuits just mentioned being connected in multiple. The other branch from the conductor 77 includes conductor 78*, where the circuit again divides, one line comprising an interlock R1 out, which bridges auxiliary contact members of the low-current limit switch C, conductors 79 and 80, an interlock marked LS1 out, directly through the standard valve magnet coil of the PK1 controller and also through a circuit that is in shunt to this coil and that includes auxiliary contact members of the high-current limit switch D and the coil of the switch RX. The other line leading from conductor 7 8 includes an interlock marked RRl out which bridges auxiliary contact members of the low-current limit switch F, conductors 81 and 82,

an interlock marked LS2 out, directly through the standard valve magnet coil of and Z1 and Z2, Bat. 1 thereby bridging the field magnet winding F1 and the resistances FBI and RX, and Bat. 2' bridging the field magnet winding F2 and the resistances F112 and KY. The switch Sv also is closed, by reason of the connection of its coil through an interlock marked PKl on to the holding conductor 37. At this stage of the control operation, a connection is established,

although the circuit is" not completed because the line switch LS1 is open, from one terminal of the switch, through the switch S, the coils of the limit switches D, B and C, the armature M; t,t1, the'field F1 in the reverse direction. the resistances FRl and BK, which are bridged by Bat. 1, the resistances R1, R2 and R3, and the switch G to ground. The motor Mil-2 is included in a similar circuit. The storage batteries serve to excite the field magnet windings with which they are asociated, and, inasmuch as the vehicle is assumed to be operating at a predetermined speed, the motors will act as generators the voltages of which are dependent upon the speed. When the circuits are in the condition just described, however, the generated electro-motive forces are somewhat lower than the electromotive force of the supply line and consequently, the dif- -f8l8l1t1fll relay switches remain down.

The PK controllers are stopped in their first operative position by reason of the breaking of the circuits of the inverted valve magnets at the contact members marked respectively PKl off and PK2 ofi'. Upon this actuation of the PK controllers, a circuit is completed from the conductor 77, through conductor 83, parallel-connected intEI-IOCkS marked, respectively, PKl on and PK2 on, conductor 84, and the conductor 60, and through the, coils of the switches M2 and G.

A circuit is then established from an energized contact member 85 of the master controller, through the control finger 42, the conductor 43, the interlock marked G in, conductor 44, the field change-over switch contact members 47 and 50 between which are interposed the auxiliary contact members of the limit switch B, the conductor 51, interlock marked LS1 out, conductor 86 and the inverted valve magnet coilof the PK1 controller to the conductors B. A similar circuit'is established from the field change-overswitch contact member 47, conductor 87, auxiliary contact members of the limit switch E, interlock marked LS2- out, and the inverted valve magnet coil of the PK2 controller to. the conductor B. Since the standard valve magnets are also energized, an independent forward step-bystep. movement of the PK controllers occurs,

thus gradually excluding the field-regulating resistance from the circuit of each motor until the voltage generated at the armature terminals thereof reaches -a predetermined value, which is in excess of the line voltage at least by an amount equal to the battery voltage, whereupon the correspondingdifierential relay switch D1 or D2 will be raised.

Upon the actuation of the D1 relay switch a circuit is completed from the conductor 79, through contact members of the relay switch, the coil of the line switch LS1 and the interlock marked M1 in to the negative conductor B. A similar circuit is closed through the coil of the line switch RX is opened at the interlock marked LS1 out, whereupon the switch is opened to insert the resistance RX in the circuit of motor M#1 at the instant of connection to the line. Moreover, the circuits of both the standard and inverted valve ma net coils of the PK1 controller are similar y broken at the interlocks marked LS1 out in the respective circuits, thereby causing a backward movement of the controller to likewise insert resistance in the circuit. In application, Serial No. 724,068, hereinbefore mentioned, only the latter means 'for preventing advantage. Moreover, the above-mentioned instantaneous insertion, in the armature circuit, of the resistor RX, together with the concurrent return of the PK1 controller toward its off position until the R2 switch closes, as hereinafter noted, causes relatively rapid exclusion of the resistors R1, R2, and R3, thereby increasing the efliciency of regeneration, as explained below. The use of such a system is claimed broadly in a copending application of Norman W. Storer, Serial No. 829,439, filed April 4 1914, and assigned to the Westinghouse lfllectric & Manufacturing Company. Various novel circuit connections that are brought about by means of this-feature, will hereinafter be pointed out.

As soon as the braking current has been caused to diminish, as just recited, sufiiciently to allow the limit switch B to assume its lower position, a circuit is established therethrough through the interlock marked LS1 in, and the interlock that is movable with the now closed switch S, to the coils of the switches R1, R2 and R3 in relatively rapid succession, dependent u on the limit ciency. Although the movement of the PK1 controller is arrested when the R2 switch closes, the closure of the following resistor switches will not be delayed, by reason of the fact that the inductance of the field winding circuit prevents the field current from following the changes in the field-circuit resistance immediately, and consequently, the effect of the insertion of the PK resistance will be felt, after the controller has stopped, for a sufficiently long time to allow the resistor switches that follow the R2 switch in the sequence of operation to be closed.

Direct connections between the coils of the R1 set of switches and coils of the RBI set are now broken at the series-connected interlcik's marked PKl off and PK2 off,

' and the coils of the BB1 set are successively energized through the limit switch E. The coil of the field change-over switch is not energized, by reason of the interruption of its circuit at the interlock marked PK2 off. However, as soon as the R3 switch is closed, a circuit is completed from contact members thereof, through conductors 88 and 86, and the coil of the inverted valve magnet of the PKl controller. A similar circuit is completed from contact members of the BB3 switch as soon as it is closed, through contact members of the field change-over switch, an interlock marked PK2 on, conductor 89, and the coil of the inverted magnet of the PK2 controller.

Upon the closure of the R1 switch, the circuit between conductors 7 8 and 7 9 is broken at the interlock marked R1 out,

- but this interlock has already been bridged,

upon connection of the motor to the line, by the low-current limit switch C. Also, upon the closure of theRQ switch, the circuit between conductor 80 and the standard valve magnet coil of the PK1 controller and coil of the switch RX is again completed by means of an interlock marked R2 in. These coils are, consequently, energized. The inverted valve magnet coil being also energized when the R3 switch closes, the PKI controller will then again move forward, dependent upon the limit switch B.

From this time, the RX switch will work in conjunction with the PK1 controller to maintain a substantially constant braking current, in the following manner. When the regenerated current diminishes to a certain value, the limit switch B will drop to allow forward movement of the PK controller. Upon the current exceeding another predetermined value, however, the limit switch D will be raised to denergize the coil of the switch RX and thus insert the resistance RX in the circuit of the motor M#l, to prevent the incipient current peak. In operation, as hereinbefore mentioned, the RX switch fiutters open and closed like the contact members of a Tirrill regulator, thereby maintaining the regenerated current within relatively narrow limits. Oscillograph records of current taken with and without the inclusion of the RX switch show the excellent current-regulating properties of the combination of the PK controller and the switch.

While I have not considered itnecessary, in every case, to describe the circuits of the motor l\/I#2, it will he understood that the circuit arrangements and connections thereof that are not specially mentioned .orrespond exactly to those of the motor Mist.

When the speed of the vehicle and consequent regenerated current falls to a relatively low value, that is, after the PK controllers have attained their last operative positions, the air brakes may automatically be set, if desired, as disclosed in the co-pending application of Serial No. 7%,068, hereinbefore mentioned. The low-current limit switches G and F will drop out, as will also the differential relay switches D1 and D2, thereby opening up the line switches and disconnecting the motors from the line.

While the master controller is provided with a braking and a holding'position, the holding position, it will be noted, differs from the braking position only in that the circuits of the inverted valve magnet coils of the PK controllers are interrupted. By this means, the progression-of the controllers may be arrested at any point and so cause the speed of the vehicle to decrease more slowly or continue at a constant speed if it is operating down hill. This enables the operator, by moving his controller from one position to the other, to regulate the rate of retardation or to hold any speed on down grade. v

While I have shown-preferred circuit connections and arrangement of parts, I wish it to be understood that variations thereof maybe madewithin the spirit and scope of my invention. ll, therefore, desire that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1. In a system of control, the combination with a supply circuit, an electric motor having an armature and afield magnet winding, a field-regulating resistance, means for separately exciting the field magnet winding, and a subdivided resistance in the armature circuit, of means for connecting the motor to the supply circuit to return energy thereto under predetermined voltage conditions, means for progressively including said fieldregulating resistance in circuit to limit the lnitially regenerated current, means for exeluding said subdivided resistance, and means for arresting the inclusion of said field-regulating resistance upon the exclusion of a predetermined amount of said subdivided resistance.

2. in a system of control, the combination with a supply circuit, an electric motor having an armature and a field magnet winding, a field-regulating resistance, means for separately exciting the field magnet winding,

and a subdivided resistance in the armature circuit, of means for connecting the motor to the supply circuit to return energy thereto when the armature voltage exceeds tie supply circuit voltage by a predetermined ire amount, electro-responsive means for pro"- gressively including said field-regulating resistance in circuit to limit the initially regenerated current, switching means for con currently excluding said subdivided of means for connecting the motor to the ing, a field-regulating separately exciting. the field magnet winddifferential relay switch for automatically connecting the motor to the supply circuit to return energy thereto when the voltage generated at the motor terminals exceeds the supply circuit voltage by a predetermined amount, fluid-pressure operated means for automatically progressively including said field-regulating resistance in circuit and limiting the initially regenerated current, means for concurrently successively actuat ing said short-circuiting switches, and contact-making means dependent upon the actuation of one of said switches for arresting the movement of" said fluid-pressure operated means.

4. In a system of control, the combination with a supply circuit an electric motor having an armature and a field magnet windresistance, means for ing, a subdivided resistance connected in the armature circuit and an auxlllary resistance,

supply circuit to return energy thereto, under predetermined voltage conditions, means for inserting said auxiliary resistance in circuit at the instant of said connection and means for concurrently and progressively including said field-regulating resistance in circuit to maintain the initially regenerated current below an excessive value, means dependent upon circuit conditions for rapidly excluding said sub-divided resistance, and means for arresting the inclusion of said field-regulating resistance when a predetermined amount of said subdivided resistance has been excluded.

5. In a system of control, thecombination with a supply circuit, an electric motor havmg an armature and a field magnet winding, a field-regulating resistance, means for separately exciting the field magnet winding, a subdivided resistance connected in the armature circuit, and an auxiliary resistance, of means for connecting the motor to the supply circuit to return energy there to when the armature voltage exceeds the supply circuit voltage by a predetermined amount, means for inserting said auxiliary resistance in circuit at the instant of said connection. an electro-responsive means for concurrently and progressively including gressively including said field-regu said fieldregulating resistance in circuit to maintain the initially regenerated current below an excessive value, means dependent? upon circuit conditions for rapidly excluding said subdivided resistance, and means for arresting the inclusion of said field regulating resistance when a predetermined amount of said subdivided resistance has been excluded.

6. In a system of control, the combination with a supply circuit, an electric motor having an armature and a field-magnet winding, a normally short-circuited field-regulating resistance, a storage battery for separately exciting the field magnet winding, a plurality of armature circuit resistors, a plurality of short-circuiting switches therefor, an auxiliary resistor, a short-circuiting switch therefor, of means for connecti said battery across said field magnet win ing and said field-regulating resistance, a differential relay switch for automatically connecting the motor to the supply circuit to return energy thereto when the voltage generated at the motor terminals exceeds the supply circuit voltage by a predetermined amount, means for opening the short-circuiting switch for said auxiliary resistor to in sert the resistor in circuit at the instant of said automatic connection, a fluid-pressure operated means for concurrently and prolating resistance in circuit to limit the initially regenerated current, means for concurrently actuating said plurality of short-circuiting switches in rapid succession, and contactmaking means dependent upon the actuation of one of said switches for arresting the movement of said fluid-pressure operated means. Y

7. A system of control for braking an electric motor comprising a supply circuit, an electric motor having an armature and a field magnet winding, a variable resistance, an auxiliary source of current, a translating device, means for connecting the said source, said resistance and said translating device in circuit with the field'magnet winding,

means for regulating the said variable resistance in accordance with the current and clectro-motive force generated by the armature, means for connecting the motor to the supply circuit when the voltage generated by the motor attains a predetermined value, means for thereupon actuating said resistance-regulating means toward its position of highest effective resistance, and means for excluding said translating device from circuit when said regulating means returns beyond a predetermined position.

8. A system of control for braking an electric motor comprising a supply circuit, an electric motor having an armature and a field magnet winding, a variable resistance, a storage battery, a resistor, means for con- '130 by the motor attains a predetermined value,.

means for thereupon returning said resistance-regulating means toward its initial operative position of highest eifective resistance, and contact-making means for excluding said translating device from clrcuit in case said regulating means causes the regenerated current to drop below a prede;

terlnined value.

In testimony whereof, I have hereunto subscribed my name this 18th day of April,

ARTHUR J. HALL. Witnesses G. R. IRWIN, B. B. HINEs. 

